total btu/h formula broken down 1

[sjdeer25]

hello i have just a general question....

the formula Q=4.5 x CFM x (delta h) i know this is standard formula at sea level but my question that i havent determuned is where does the 4.5 constant get derived from..what are the specifics of that constant and does it change upon ones change in elevation.

 

[MintJulep]

It contains all of the things that are needed to make the units work out.

Things like density, specific heat and 60 are in there.

 

[DUMechEng]

q (btu/hr) = mass flow (lb/hr) x enthalpy change (btu/lb)

mass flow (lb/hr) = volume flow (cf/hr) x density (lb/cf)

60 mins = 1 hour
air density at standard conditions = 0.075 lb/cf

so...

q (btu/hr) = volume flow (cf/min) x 60 (min/hr) x 0.075 (lb/cf) x enthalpy change
or
q = 4.5 x CFM x enthalpy change

altitude, moisture content, and temperature will all affect the 4.5 constant because they all affect density.